1. Field of the Invention
This invention relates to a fixture for a friction pad and its operational method used for applying pressure on the circumferential surface of a paper feeding roller provided in image forming apparatus like copiers, printers, facsimile devices and the like to prevent copy papers from being fed in duplication.
2. Description of the Prior Art
There has been conventionally known a fixture arrangement of this kind for a friction pad used for copiers as shown in FIG. 5.
In the conventional fixture arrangement A shown above, as shown in FIG. 5, a friction pad 12 is disposed at a location on a frame 7' which is located opposite to a paper feed roller 8 provided on a snatch frame 7 of a clam shell type. The friction pad 12 is secured to a pad holder 13 that is supported vertically movable in a mounting opening 11 carved on the surface of said frame 7' and is always elastically urged against the paper feed roller 8 by a spring not shown.
At an upper portion of said frame 7' there is provided an advancing feed roller 30 whose outer circumferential surface comes in contact therewith. This advancing feed roller 30 is provided for feeding copying papers carried on a stack table 9 into a nipping area between said paper feed roller 8 and said friction pad 12. There is a well known advancing feed roller 30 such as the one just mentioned, which is actuated to rotate continuously until a copying process has been completed once the copy button is depressed regardless of the presence of copying papers on said stack table 9.
The friction pad 12 is replaced when worn out excessively than the specified amount by the frictional encounter with copying papers to prevent faults such as paper feeding error or abnormal noise.
In the conventional fixture arrangement A thus constructed, however, to replace the friction pad 12 requires the removal of the paper feed roller 8 from the frame 7 and further, the disassembly of parts including a pad holder 13 and the spring not shown within the mounting opening 11 since they are assembled within said mounting opening 11 together with the friction pad 12 as shown above.
This structure necessitates a high skill to replace the friction pad 12, which is then conventionally performed by a service engineer dispatched from a manufacturer involved.
The arrangement of the paper feed roller 8 and the friction pad 12 as shown above aims at sorting a plurality of copying papers inserted between them by the advancing feed roller 30 and advancing only one paper that is nearest the paper feed roller 8 (the uppermost one).
The duplication-free handling of copying papers like this is performed in such a way that the difference in coefficient of friction among the paper feed roller 8, copying paper, and friction pad 12 is utilized to feed the uppermost paper by the paper feed roller 8 while braking is applied to the carry of copying papers by the friction pad 12. Because of this there occurs a duplication paper feed when different frictional forces among these three elements (according to the difference in coefficient of friction) mentioned above change. The difference in these frictional forces will slightly change according to the pressure applied to the paper feed roller 8 by the friction pad 12 (pad pressure), the material of the pad as well as the kind of copying papers used.
However, since a highly skillful technique is required to replace the friction pad in the conventional fixture arrangement for the same, users cannot readily replace the currently used friction pad with the one optimum for another kind of paper to be used or adjust the pad pressure, a service engineer is required every time such an operation is performed.
The present invention is, therefore, aiming at eliminating the above mentioned problems and providing an improved fixture for a friction pad and its operational method in which the replacement of the friction pad or adjustment of the pad pressure is readily performed by an operator without the help of a service engineer.